The research team, led by Ali Nouri together with Hassan Heidari and Farzad Mondani from the Department of Plant Production and Genetics, set out to answer a question that matters enormously for rain-fed agriculture: how can farmers squeeze more oil out of the same amount of precipitation? Their answer came from a rigorously designed field experiment conducted at two locations, Kermanshah and Kangavar, using a split-plot arrangement within a randomized complete block design with three replications. This statistical architecture allowed the researchers to isolate the effects of two factors independently and to test whether they interact, a crucial consideration when combining soil management practices with nutrient inputs.

The experimental design was straightforward but comprehensive. Nitrogen fertilizer, supplied as urea, was applied at four levels: zero, 40, 80, and 120 kilograms of nitrogen per hectare. Plastic mulch, meanwhile, was evaluated in three configurations: no mulch at all, mulch placed over the plants themselves, and mulch laid directly on the soil surface. This distinction between covering the plants and covering the ground is more than a technicality. Mulch on soil works primarily by suppressing evaporation, trapping soil moisture beneath a physical barrier and moderating soil temperature, whereas mulch over plants alters the crop’s microclimate in ways that can affect transpiration and light interception. By testing both, the team could determine which strategy delivered the greatest physiological benefit to camelina under rain-fed conditions.

The results were unambiguous. Increasing nitrogen application and deploying plastic mulch, whether on the soil or over the plants, led to consistent increases in rainfall productivity, protein yield, oil yield, and the content of chlorophyll b, the photosynthetic pigment that harvests light in plant chloroplasts. The highest values for protein yield, oil yield, and chlorophyll b were all recorded in plots receiving 120 kilograms of nitrogen per hectare combined with plastic mulch laid on the soil. At the opposite extreme, the untreated control plots, which received no nitrogen and no mulch, produced the lowest values across all three measures. The pattern suggests that water conservation and nutrient supply act synergistically: neither input alone unlocks the crop’s full potential, but together they create conditions in which camelina can convert both sunlight and scarce moisture into oil far more efficiently.

One of the most striking physiological findings concerned leaf relative water content, a measure of how well hydrated plant tissue remains under field conditions. In plots receiving 120 kilograms of nitrogen per hectare, leaf relative water content was 12.6 percent higher than in the control treatment. This matters because water status is tightly linked to photosynthetic performance: when leaf tissue dries, stomata close, carbon dioxide uptake falls, and the biochemical machinery of photosynthesis slows. Higher relative water content indicates that the mulched, well-fertilized plants were under less drought stress, allowing them to sustain carbon fixation through the growing season and channel more of that fixed carbon into seed production and oil accumulation.

The study also documented changes in the plants’ stress biochemistry. Proline, an amino acid that accumulates in plant tissues as a compatible solute during water stress, was elevated in the treatments associated with better overall performance, and the researchers linked the improved oil yields to a suite of favorable physiological traits including rainfall productivity, chlorophyll b content, and proline dynamics. Carotenoid levels, another class of photosynthetic and photoprotective pigments, rose alongside nitrogen and mulch treatments. Together, these indicators paint a picture of plants that were better equipped to capture light, protect their photosynthetic apparatus, and maintain cellular function under the moisture limitations inherent to rain-fed farming.

Nutrient uptake told a parallel story. Raising the nitrogen level and applying plastic mulch led to higher concentrations of nitrogen, phosphorus, and potassium in the camelina seeds, along with greater leaf relative water content. This is significant for more than agronomic bookkeeping. Seed nitrogen translates directly into protein content, which affects the value of the meal left over after oil extraction as an animal feed. Phosphorus and potassium play central roles in energy transfer and enzyme regulation, and their enhanced accumulation in seeds suggests that improved soil moisture under mulch made these nutrients more available for uptake by roots. Water and nutrient cycling in dryland soils are deeply intertwined: nutrients move to root surfaces largely in the water film of moist soil, so conserving moisture effectively fertilizes the crop indirectly by keeping nutrient transport pathways open.

The concept of rainfall productivity sits at the heart of the study’s practical significance. In regions where crops depend entirely on precipitation rather than irrigation, the yield of a field is ultimately limited by how efficiently each unit of rain is converted into harvestable product. By measuring rainfall productivity alongside oil yield, the researchers framed their findings in terms that matter to dryland farmers and to anyone concerned with water-limited food and fuel production. The combination of soil-surface plastic mulch and 120 kilograms of nitrogen per hectare maximized this conversion efficiency, meaning the same seasonal rainfall yielded more oil per hectare than under any other treatment combination tested.

For the biofuel and biodiesel sectors, the implications are noteworthy. Camelina has attracted attention as a low-input oilseed that can be grown on land unsuitable for food crops, reducing competition between fuel and food production. Its short growing season and tolerance of cold and drought make it a candidate for rotation with wheat in dryland systems. However, yields in water-limited environments have often been modest, limiting the crop’s economic appeal. Demonstrating that a relatively inexpensive intervention, plastic sheeting on the soil, combined with an optimized nitrogen rate can lift oil yield and protein yield simultaneously addresses both the energy and the co-product value chains. The researchers’ recommendation is specific: for conditions similar to those at their Iranian field sites, plastic mulch on the soil with nitrogen at 120 kilograms per hectare is the treatment of choice for achieving the highest camelina oil yield.

Caveats remain, as they always do in field research conducted at two sites within a single climatic zone. The optimal nitrogen rate and mulch configuration could shift under different rainfall patterns, soil types, or economic conditions, and the environmental footprint of plastic mulch, including questions of removal and disposal, is a consideration the broader literature continues to debate. The study received no specific grant funding, and the authors declare no competing interests. Yet the core message is robust and immediately actionable: in dryland agriculture, managing water and nutrients together, rather than in isolation, is the key to unlocking the productivity of crops like camelina. As demand grows for vegetable oils that do not compete with food production, findings like these offer a concrete path toward making marginal rainfall yield more oil, one covered hectare at a time.

Subject of Research: Effects of plastic mulch and nitrogen fertilizer on oil yield and rainfall productivity of rain-fed camelina

Article Title: Improving rainfall productivity and oil yield in camelina through the use of plastic mulch and nitrogen

Article References: Nouri, A., Heidari, H., & Mondani, F. (2026). Improving rainfall productivity and oil yield in camelina through the use of plastic mulch and nitrogen. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10086-8

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10086-8

Keywords: camelina, plastic mulch, nitrogen fertilizer, rainfall productivity, oil yield, dryland agriculture, biodiesel, chlorophyll b, proline, soil moisture, urea, Razi University

The study, published in Plant Cell Reports, centers on a gene called EgKT2-1, which encodes a Shaker-type potassium channel in the African oil palm, Elaeis guineensis. Shaker channels are the workhorses of potassium transport in plants, voltage-dependent pores embedded in the plasma membrane that move massive fluxes of the ion across long distances. Each channel subunit carries six transmembrane segments, including a voltage sensor and a highly selective pore lined by the conserved TXXTXGYGD amino acid motif, plus a large intracellular tail bearing cyclic nucleotide-binding, ankyrin and KHA domains. Four subunits must assemble into a tetramer to form a functional pore, and the identity of those subunits determines whether the channel carries potassium into the cell, out of it, or in both directions depending on membrane voltage.

Using the oil palm reference genome, the researchers catalogued the entire Shaker channel family and found eight members, a count matching date palm and coconut but differing from the nine channels of Arabidopsis and ten of rice. Intriguingly, palms lack the silent, regulatory Group IV subunits found in many model plants, and they possess two members of the AKT2-like Group III subfamily, EgKT2-1 and EgKT2-2, where Arabidopsis and rice each carry only one. Sequence analysis placed EgKT2-1 squarely within the AKT2-like family, channels that typically behave as weak rectifiers, allowing potassium to flow both into and out of the cell. What happened next defied that expectation.

When the team expressed EgKT2-1 in Xenopus laevis oocytes and clamped the membrane voltage across a range from +70 to −170 millivolts, the channel produced large, time-dependent inward currents with the sigmoidal activation kinetics characteristic of plant inward rectifiers. Inward currents reached amplitudes of up to −25 microamperes, while outward currents were essentially negligible even at low external potassium. In other words, despite its family pedigree, EgKT2-1 functions as a one-way valve for potassium uptake, not a bidirectional conduit. The activation threshold sat near −50 millivolts, and current amplitude grew with external potassium concentration, confirming a genuine potassium-dependent conductance. The channel showed strong selectivity, passing rubidium only partially and carrying almost no current with sodium or lithium, and its activity was blocked by the classic potassium channel inhibitors cesium and barium, which suppressed currents by 75 and 80 percent respectively at −170 millivolts.

The atypical behavior has a plausible structural explanation. In rice, the OsAKT2 channel also behaves predominantly as an inward rectifier, and site-directed mutagenesis showed that a single lysine residue in the voltage-sensing S4 domain is a major determinant of that rectification. EgKT2-1 carries a lysine at the corresponding position, K195, whereas Arabidopsis AKT2 has two consecutive arginines there. The comparison suggests that weak rectification is not a universal property of AKT2-type channels but depends on specific amino acids within the voltage sensor. Equally puzzling was what the team did not find: unlike several AKT2 orthologs whose activity is dampened by external acidification, EgKT2-1 was indifferent to pH changes between 5.5 and 7.5, even though the residues previously implicated in proton sensitivity in Arabidopsis are conserved in the palm channel. That insensitivity remains unexplained and will require further structural work.

Where the gene is switched on proved just as revealing as how its protein behaves. Quantitative PCR showed EgKT2-1 transcripts abundant in leaves and shoot meristems of young palms, and in adult trees, expression peaked in leaves and in fruits during early development, between 30 and 60 days after anthesis, a window when fruit size and mass expand rapidly and when potassium content in the mesocarp is known to climb. Expression was low in flowers, roots, rachis, and in fruits at mid-ripening around 120 days after anthesis or maturity around 160 days. In situ hybridization sharpened the picture: in roots, transcripts localized to the cortex, phloem and pericycle cells adjacent to xylem poles, consistent with a role in potassium uptake and radial transport toward the vascular cylinder; in leaves, signals appeared in palisade parenchyma cells of the mesophyll, hinting at a contribution to photosynthetic tissue function; and in fruits, transcripts were detected exclusively in mesocarp cells at 60 days after anthesis, precisely the stage of peak potassium accumulation.

The timing matters because potassium is deeply entwined with the biochemistry of oil. As the most abundant cytosolic cation in plant cells, potassium activates enzymes, sustains turgor, drives phloem sap circulation and regulates stomatal opening. Among the enzymes it supports are pyruvate kinase and pyruvate dehydrogenase, which supply precursors for fatty acid synthesis. Earlier work on oil palm showed that low potassium availability perturbs pyruvate and mesocarp metabolism during fruit development, and that mesocarp potassium content rises through the first 105 days after anthesis before declining as lipid biosynthesis takes over. A channel that loads potassium into mesocarp cells during that early window could therefore help set the metabolic stage for the oil accumulation that follows, and strict inward rectification would be advantageous, favoring influx at negative membrane potentials while limiting losses under depolarized conditions.

The most striking result came from a field comparison. The researchers studied two oil palm progenies, C2 and C3, both derived from the same Deli by La Mé parental cross and grown under identical potassium fertilization at a plantation in Nigeria. Previous agronomic work had established that C3 produces significantly more bunches and more oil than C2 and allocates more potassium to its aerial organs. When the team measured EgKT2-1 expression in developing fruits, they found it nearly fourfold higher in C3 than in C2. The correlation is tantalizing: a channel that ferries potassium into the oil-rich flesh of the fruit is more active in the progeny that yields more oil. It raises the possibility that EgKT2-1 expression could serve as a molecular marker for oil production traits, potentially allowing breeders to screen young palms for high-yield potential before years of field trials.

The authors are careful, however, not to overclaim. The yield association rests on a comparison of just two progenies, and other genetic differences between them could equally explain the phenotypic gap, so the data establish a correlation rather than a causal link between EgKT2-1 and oil accumulation. The oocyte experiments prove the protein is an inward potassium channel, but its impact on oil biosynthesis in living palms remains inferred. Validation in larger, genetically diverse breeding populations, together with genetic approaches such as transgenic or CRISPR-based manipulation of EgKT2-1 expression, will be needed to test whether the channel directly drives yield differences. Still, the study delivers the first functional portrait of a Shaker channel in oil palm and opens a concrete path toward a longstanding goal: breeding palms that squeeze more oil from every kilogram of fertilizer, easing both the economics and the environmental footprint of the world’s most productive oil crop.

Subject of Research: Functional characterization of the Shaker-type potassium channel EgKT2-1 in oil palm and its correlation with potassium allocation and oil yield

Article Title: EgKT2-1, an inwardly rectifying Shaker-type potassium channel in oil palm that correlates with oil yield

Article References: Monder, H., Espeout, S., Zimmermann, S. D., Billotte, N., Verdeil, J.-L., Bocs, S., Ollivier, J., Impens, R., Jacob, F., Gaillard, I., & Cuéllar, T. (2026). EgKT2-1, an inwardly rectifying Shaker-type potassium channel in oil palm that correlates with oil yield. Plant Cell Reports, 45(10), Article 315. https://doi.org/10.1007/s00299-026-03975-7

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03975-7

Keywords: oil palm, Elaeis guineensis, potassium channel, Shaker channels, EgKT2-1, inward rectifier, potassium transport, mesocarp, fruit development, oil yield, electrophysiology, plant breeding